The spikes and plates of the Jurassic Stegosaurus may look like armor
that could have staved off intrepid predators, but defense most likely was not
their main purpose. According to new research, these bony growths on the back
and tail were actually meant for species recognition  so that one
Stegosaurus could pick its friends out of a crowd.

Paleontologists have been trying to determine what the plates and spikes
of stegosaurs were for, for over a century, says Russell Main, lead author
of a new study published in Paleobiology in May. The hypotheses
have included defense, thermoregulation and display, either sexual or species
recognition.